Technical Abstract:
For managed disturbances, such as military training activities or recreational use, a sustainable disturbance regime allows ecosystems to recover to predisturbance conditions between disturbance events. In arid environments, recovery from disturbance typically requires long time periods. Furthermore, disturbance may alter vegetation dynamics such that thresholds are crossed and a shift in dominance from grasses to shrubs is observed. Such a shift in dominance is considered irreversible under current climatic conditions because of positive feedback mechanisms between the biotic and abiotic environment. Disturbance management in arid lands depends on knowledge about recovery time and thresholds in system dynamics. The objective of this study was to investigate how recovery time and susceptibility to a change in dominance vary between vegetation types in southern New Mexico. We used an individual-based simulation model (ECOTONE) to simulate disturbances with different timing with respect to climate events, different sizes, and different intensities in desert grasslands and shrublands. Both vegetation types recovered easily from low intensity disturbances. Recovery time on large disturbance was determined by the seed dispersal distance of the dominant species. Disturbances with high intensity in grasslands caused a shift in dominance from grasses to shrubs. The probability of such a shift in dominance depended on the timing of the disturbance with regard to climatic events and soil type. These results correspond to observations on vegetation dynamics after disturbance in southern New Mexico. Using this model, we were able to refine disturbance management recommendations for desert grasslands and shrublands.